1. Field of the Invention
The invention relates to protecting read/write heads of magnetic disk drives from electrostatic discharge (ESD) during manufacture, and more particularly to methods and a structure for preventing dielectric breakdown during magnetoresistive (MR) and giant magnetoresistive (GMR) head fabrication.
2. Description of the Related Art
In a state-of-the-art magnetic disk drive a magnetic transducer, referred to as a read/write head, is formed integrally with a xe2x80x9csliderxe2x80x9d. The slider flies over a rotating disk, thus allowing the read/write head to record/retrieve information to and from a thin film of magnetic medium, which is coated on the disk. The read portion of the transducer, referred to as a read head, consists of a thin layer of MR or GMR sensor stripe sandwiched between two magnetic shields. A constant current is passed through the sensor stripe, whose resistance varies in response to a previously recorded magnetic pattern. Thus a corresponding varying voltage is detected across the sensor stripe. The magnetic shields help the sensor stripe to focus on a narrow region of the magnetic medium, hence improving the spatial resolution of the read head. The space between the shields is called the read gap.
The magnetic shields are electrically conductive. To prevent the sensing current from leaking into the shields, a thin dielectric film insulates the sensor stripe from each shield. However, if the electric potentials differ sufficiently across any of the two dielectric films, the dielectric film will break down, and the read head will be destroyed. Such undesirable destruction occurs quite often in the fabrication of read heads for two reasons. First, the sensor stripe and the shields are deposited and patterned by electrical processes in the vacuum, such as sputtering or ion-beam. Static charge inevitably builds up on all isolated surfaces. Thus an electrostatic field exists between isolated conductors situated at different depth of the wafer, for example between the sensor stripe and the shields. Attempts to neutralize the static surface charge are tedious, costly, and with limited success. Secondly, the read gap is extremely thin (for example, about 150 nm, where n stands for nano or 10xe2x88x929) in the state-of-the-art read/write heads, in order to achieve high resolution. Correspondingly, the dielectric films are even thinner (for example, a mere 20 nm). These dielectric films can break down under a few volts, and cause electrostatic discharge (ESD) which permanently damages the read sensor. As the magnetic recording technology advances, the dielectric films continue to become thinner and more susceptible to the static charge buildup and dielectric breakdown.
The read/write heads are produced en masse in the form of a wafer. Typically each wafer contains over 10,000 heads. A finished wafer is subsequently cut into rows and further diced into sliders. The surface of a read/write head facing the disk medium, known as the air bearing surface (ABS), is created when the wafer is cut into rows. The ABS is subsequently polished to achieve a precise MR stripe height, and etched to form an intricate pattern which is needed in order for the slider to fly on the disk. A finished slider is mounted on an elastic structure, referred to as a suspension. The suspension is then assembled into a disk drive. In each of the above processes, a read head is susceptible to ESD. Even in a finished disk drive, the performance of a read/write head can be adversely affected by static charge buildup on the magnetic medium. Numerous workers in the field have sought solutions to these problems, as demonstrated by the following U.S. patents:
U.S. Pat. No. 5,465,186 (Bajorek et al.) teaches a method for shunting MR by soldering the lead terminals at the slider surface, thereby diverting transient current during ESD events.
U.S. Pat. No. 5,491,605 (Hughbanks et al.) shows the leads of the MR read head and inductive write head shunted together and connected to the slider substrate through a conductive layer at the ABS.
U.S. Pat. No. 5,699,212 (Erpelding et al.) places solder shunts across adjacent leads of the MR read head, on the suspension. In this and the above two patents, the shunts must be removed before operation of the read/write head.
U.S. Pat. No. 5,757,590 (Phipps et al.) describes removable fusible-links to shunt the MR sensor stripe. The shunts can be opened by electrical means.
U.S. Pat. No. 5,539,598 (Denison et al.) teaches an arrangement wherein each magnetic shield is connected to a ground lead of the MR sensor, through a resistor deposited with the MR sensor stripe.
U.S. Pat. No. 4,802,043 (Sato et al.) describes connections between a sensor stripe and both magnetic shields, through an electrical lead.
Note that U.S. Pat. Nos. 5,465,186, 5,491,605, 5,699,212, and 5,757,590 alleviate problems caused by static buildup after wafer fabrication. None of them provides any protection against static buildup during wafer fabrication of the MR or GMR read heads. U.S. Pat. Nos. 5,539,598 and 4,802,043 do describe electrical connections between the sensor stripe and the shields within the wafer. However, the connections are established too late in the wafer fabrication. In both U.S. Pat. Nos. 5,539,598 and 4,802,043, the sensor stripe and the shields are deposited and patterned as isolated conductors before they are connected to each other. In the state-of-the-art MR/GMR sensors, the dielectric films are too thin to withstand the static charge buildup during the deposition and patterning of the sensor stripe and the second (upper) magnetic shield. The dielectric films often break down before the sensor stripe is connected to either shield. Therefore, the patents cited above did not solve the problem of dielectric breakdown during wafer process.
In addition, U.S. Pat. Nos. 5,539,598 and 4,802,043 establish permanent electrical connections between the MR sensor and two magnetic shields. In some applications, the sensor stripe must be isolated from the shields before the slider is assembled into a disk drive. This is usually due to the concern that electrical noise from the write head may couple capacitively into the shields. For these applications, the permanent connections described in U.S. Pat. Nos. 5,539,598 and 4,802,043 are unacceptable. A removable MR-to-shield connection is needed to provide ESD protection during wafer fabrication and slider processes.
It is an object of the present invention to provide methods and a structure to avoid dielectric breakdown during the wafer fabrication of MR or GMR read heads of magnetic disk drives.
Another object of the present invention is to avoid dielectric breakdown, without excessively stringent requirements on charge neutralization during wafer fabrication of MR or GMR read heads.
A further object of the present invention is to provide methods and a structure for the manufacture of MR or GMR read heads having an isolated read-stripe free of defects from dielectric breakdown.
These objects have been achieved by depositing the sensor stripe and the magnetic shields contiguously as an integral conductor. In the present invention, the sensor stripe and the magnetic shields are never electrically isolated from each other during the entire wafer process. The sensor stripe and the magnetic shields are always kept in equipotential. Therefore, the risk of dielectric breakdown is eliminated. The electrical connections between the sensor stripe and the magnetic shields are severed only after the wafer process is complete.